[sdiy] TR-909 schematic/PCB error

rburnett at richieburnett.co.uk rburnett at richieburnett.co.uk
Sun Nov 13 14:18:27 CET 2016

For anyone who has one of Trevor Page's TR-9090 boards, you should be 
able to modify it match a TR-909 by either:

1. Cut a track and patch the RS output signal from IC50a's output with a 
short length of wire, instead of from IC50b's output.

...or alternatively...

1. Short circuit components C121, C122, R421, (or fit links in their 
places, if these components haven't been fitted yet.)
2. Leave R419, R420, R422 in place, (or no need to fit them if they 
haven't been soldered already.)

This will turn IC50b from a high-pass filter into a unity gain buffer, 
essentially rendering it sonically inert.

The modified rimshot sound should have more bass presence and more CV 
feed-through from the VCA than when passed through the HPF.


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